Loft boarding - Truss, Brace, Kings & Queens

[Wayners]

I had those diagonal timbers on my loft conversion and I wish I removed them.
Caused me trouble as I had to pack out every joist with 22mm batten before cross battening on the inside. I don't think it's the right way to go about it and very little knowledge from those I asked on how it should be done.

It's my understanding that if roof tiles and felt is replaced you need wood cross timbers on the inside to hold roof together. That's what those cross timbers do.
I fitted them as roof trusses where dropped on with the crain.

Seems the American way is fit 8x4 boards inside to hold trust timbers which is what I'd of done had I known.
Stagger them as well and butt against the wall.

Also be aware that loft boards are a pain to remove to get to the cables and pipes. I've spent hours struggling with loft boards.
I've also seen many lofts overloaded with stuff.

Consider some floorboards in the main area and put shelves up on that wall.
Always ware a mask. Not a great place to spend time in with fibreglass and dust

 

[brennan2470]

I had those diagonal timbers on my loft conversion and I wish I removed them.
Caused me trouble as I had to pack out every joist with 22mm batten before cross battening on the inside. I don't think it's the right way to go about it and very little knowledge from those I asked on how it should be done.

It's my understanding that if roof tiles and felt is replaced you need wood cross timbers on the inside to hold roof together. That's what those cross timbers do.
I fitted them as roof trusses where dropped on with the crain.

Seems the American way is fit 8x4 boards inside to hold trust timbers which is what I'd of done had I known.
Stagger them as well and butt against the wall.

Also be aware that loft boards are a pain to remove to get to the cables and pipes. I've spent hours struggling with loft boards.
I've also seen many lofts overloaded with stuff.

Consider some floorboards in the main area and put shelves up on that wall.
Always ware a mask. Not a great place to spend time in with fibreglass and dust

This is actually a garage so no need to worry about cables, pipes or insulation but same principle applies re the diagonal braces on the truss chords. They don’t appear to be doing anything structurally because the chords are already braced longitudinally along the bottom of the webs and diagonally in a chevron pattern across the rafters.

My garage roof trusses were also craned in therefore presumably that’s why those braces are still there, more work for them to remove them! I think it should be fine to remove them but thought I would get a general consensus first.

 

[^woody^]

Do you know of any requirement to brace the truss chords if the rafters have chevron bracing? My chords are braced diagonally but I am unsure if I can remove them when I build an independent mezzanine floor which will involve adding 8x2 joists adjacent to (but not connected to) the existing truss cords.

I assume these braces are merely there to spread the load of somebody walking along the truss chords, which I won’t be doing, so can be removed? Cheers

Yes the bottom chords need bracing along with the top chords. Typically this is a longitudinal timber where the web meets the bottom chord, and prevents flexing of the truss.

Potentially that function could be replicated in another way as long as the bottom chords are kept rigid and in unison.

 

[brennan2470]

Yes the bottom chords need bracing along with the top chords. Typically this is a longitudinal timber where the web meets the bottom chord, and prevents flexing of the truss.

Potentially that function could be replicated in another way as long as the bottom chords are kept rigid and in unison. are braced

My question is whether these chords needs to be for diagonally braced (which they are) in addition to the longitudinal braces along the chords where the web meets, or whether these diagonal braces were simply there for temporary reasons whilst battening and tiling and just haven’t been removed.

 

[catlad]

If I where you I would replicate what you have now under the cords with what you have now. Once you have built your new floor you could remove the new bracing if you wished.

 

[brennan2470]

If I were you I would replicate what you have now under the cords with what you have now. Once you have built your new floor you could remove the new bracing if you wished.

The problem I have is the new joists start 5” below the current chords and finish level with the top of the chords (3”, so 8” in total). My preference would just be to remove the diagonals if they aren’t required and retain the longitudinals

 

[^woody^]

My question is whether these chords needs to be for diagonally braced.

Typically this is a longitudinal timber where the web meets the bottom chord,

 

[brennan2470]

thanks for your help. The garage is 7m deep by 6m wide. I was intending on running 7m 8x2 joists front to back between the existing truss chords using joist hangers and then 3x 6m perpendicular beams consisting of 2x 2x10’s bolted together secured to the gable ends with heavy duty joist hangers bolted together the wall with resin anchors.

Is that sufficient to carry 42sqm of 22mm chipboard and 12.5mm plasterboard, plus all my gear stored up there, or is there a better way of achieving this which I’m missing?

 

[catlad]

Do you have the option of putting a beam under the cords to achieve greater strength for storage?

 

[brennan2470]

Do you have the option of putting a beam under the cords to achieve greater strength for storage?

I do, in fact I was planning to add 3 beams of 90x250 to support the new joists I intended to run anyway. Most of what I read was to leave the chords/trusses alone and build a completely independent floor, but I’m open to ideas. Bear in mind the dimension perpendicular to the chords is 6m so it’s a relatively meaty span.

 

[catlad]

I feel you maybe going a little over the top. What are you planning on storing ie. weights wise and how will you create the space for storage?

 

[brennan2470]

I feel you maybe going a little over the top. What are you planning on storing ie. weights wise and how will you create the space for storage?

Well my concern was that 22mm chipboard over ~40sqm was going to be about 750kg, then 15 sheets of plasterboard around 350kg. That’s before I even store stuff up there.

Storage wise the usual stuff, kids stuff, outdoor furniture cushions, lots of paint tins, camping and leisure stuff and just general boxes of bits.

Given the sheer amount of space it would create I wouldn’t need to worry too much about building racking, most of the stuff could just be stored on the deck itself between each ‘W’ truss and accessed via the main gangway.

My main concern is significant deflection over such long spans (7m front to back) causing the plasterboard to crack, or worse, the entire thing be unsafe, which is why I was planning on having 3 90x250 beams spread equidistant along the 7m spans, but even then those perpendicular spans will be 6m so well out of the joist span tolerances.

I have the DIY skills and the tools to carry all of this out, but obviously it’s impossible for me to know how structurally sound this would be (given I need to walk around up there). Some might say it’s over engineered but according to joist span tables it’s incredibly under engineered, so I’m just trying to figure out how best to approach this.

Whatever suggestions you can provide for a 6x7m trussed garage would be much appreciated.

 

[catlad]

then 15 sheets of plasterboard around 350kg.

Sorry I must have misunderstood, I thought you just wanted to strengthen the ceiling for storage.

 

[brennan2470]

Sorry I must have misunderstood, I thought you just wanted to strengthen the ceiling for storage.

Yes predominantly. Plasterboarding isn’t a must

 

[catlad]

From your pictures there is a pile of insulation, what s the ceiling now?